Data from: Shear-sensitive adhesion enables size-independent adhesive performance in stick insects

The ability to climb with adhesive pads conveys significant advantages,
and is hence widespread in the animal kingdom. The physics of adhesion
predict that attachment is more challenging for large animals, whereas
detachment is harder for small animals, due to the difference in
surface-to-volume ratios. Here, we use stick insects to show that this
problem is solved at both ends of the scale by linking adhesion to the
applied shear force. Adhesive forces of individual insect pads, measured
with perpendicular pull-offs, increased approximately in proportion to a
linear pad dimension across instars. In sharp contrast, whole-body force
measurements suggested area-scaling of adhesion. This discrepancy is
explained by the presence of shear forces during whole-body measurements,
as confirmed in experiments with pads sheared prior to detachment. When we
applied shear forces proportional to either pad area or body weight, pad
adhesion also scaled approximately with area or mass, respectively,
providing a mechanism that can compensate for the size-related loss of
adhesive performance predicted by isometry. We demonstrate that the
adhesion-enhancing effect of shear forces is linked to pad sliding, which
increased the maximum adhesive force per area sustainable by the pads. As
shear forces in natural conditions are expected to scale with mass,
sliding is more frequent and extensive in large animals, thus ensuring
that large animals can attach safely, while small animals can still detach
their pads effortlessly. Our results therefore help to explain how
nature’s climbers maintain a dynamic attachment performance across seven
orders of magnitude in body weight.